An arrhythmia is any heartbeat that doesn’t follow the normal rhythm. Your heart might beat too fast, too slow, or with an irregular pattern. A normal resting heart rate falls between 60 and 100 beats per minute, and an arrhythmia is what happens when the electrical signals controlling that rhythm misfire. Some arrhythmias are harmless and last only seconds. Others can stop blood flow to the body and become life-threatening within minutes.
How Your Heart’s Electrical System Works
Your heart has four chambers: two upper chambers (atria) and two lower chambers (ventricles). Every heartbeat starts with an electrical signal fired by a cluster of cells at the top of the heart called the sinus node. That signal travels down through a gateway between the upper and lower chambers, triggering each section to contract in sequence. The upper chambers squeeze first, pushing blood into the lower chambers. Then the lower chambers squeeze, pumping blood out to the lungs and the rest of the body.
An arrhythmia occurs when something disrupts this electrical pathway. The signal might fire too quickly, too slowly, or from the wrong location. It might also get stuck in a loop, causing part of the heart to quiver instead of contracting with force. When the heart can’t pump blood efficiently, organs and tissues don’t get the oxygen they need.
Types of Arrhythmia
Arrhythmias are grouped by where they start in the heart and how they affect heart rate.
Too Fast (Tachycardia)
A resting heart rate above 100 beats per minute is considered tachycardia. Types that start in the upper chambers include atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia (PSVT). Atrial fibrillation is the most common arrhythmia overall, with roughly 4.48 million new cases diagnosed globally in 2021. During an episode, chaotic electrical signals can push the upper chambers to fire more than 400 times per minute. The upper and lower chambers fall out of sync, and the heart can’t pump blood effectively.
Atrial flutter is similar but more organized, with the upper chambers beating 250 to 350 times per minute. PSVT starts and stops suddenly, often during vigorous exercise. It’s more common in young people and typically isn’t dangerous.
Tachycardias that start in the lower chambers are more serious. Ventricular tachycardia produces a fast, regular beat in the ventricles. A few seconds of it may cause no harm, but if it persists, it can progress to ventricular fibrillation. In ventricular fibrillation, the lower chambers quiver instead of pumping. Blood stops flowing. Without treatment, cardiac arrest and death can follow within minutes.
Too Slow (Bradycardia)
A resting heart rate below 60 beats per minute is bradycardia. For well-trained athletes, this can be perfectly normal. In other cases, it signals that the sinus node isn’t firing correctly or that electrical signals are getting blocked before reaching the lower chambers. Symptoms tend to appear when the rate drops below 40 or so, especially if you feel dizzy, faint, or short of breath.
What Causes an Arrhythmia
Arrhythmias can stem from structural problems, chemical imbalances, or outside triggers. Damage to heart tissue from a previous heart attack, heart disease, or congenital defects can create scar tissue that disrupts electrical pathways. High blood pressure, diabetes, and problems with heart valves also raise the risk.
Electrolyte imbalances are a well-documented trigger, particularly low potassium. In one study of patients who arrived at the hospital with dangerous ventricular arrhythmias, nearly 36% had low potassium levels, compared to about 13% of heart failure patients without arrhythmias. Gastrointestinal illness (vomiting or diarrhea) and recent increases in diuretic doses were strongly associated with severe potassium depletion in these patients.
Everyday substances play a role too. Caffeine, nicotine, amphetamines, and cocaine can all speed up electrical activity in the heart. Over-the-counter cold and allergy medicines that contain stimulants can do the same. Alcohol is another common trigger, particularly for atrial fibrillation. Sleep apnea, uncontrolled high blood pressure, and high cholesterol also contribute to long-term risk.
Symptoms to Recognize
Many arrhythmias produce no symptoms at all and are only discovered during a routine checkup. When symptoms do appear, they typically include palpitations (a fluttering or pounding sensation in your chest), dizziness or lightheadedness, shortness of breath, chest pain, sweating, paleness, and fainting. You might feel like your heart is racing, skipping beats, or flip-flopping in your chest.
The severity of symptoms depends on the type of arrhythmia and how much it affects blood flow. A few extra beats from the upper chambers might feel like a brief flutter and nothing more. Ventricular fibrillation, on the other hand, causes loss of consciousness within seconds.
How Arrhythmias Are Diagnosed
If your symptoms happen consistently, a standard electrocardiogram (ECG) recorded in a clinic can capture the irregular rhythm in real time. The test takes a few minutes and involves small sensors placed on your skin that detect your heart’s electrical activity.
The challenge is that many arrhythmias come and go. If an ECG looks normal at your appointment, your doctor may send you home with a Holter monitor, a portable device about the size of a small phone that records your heart rhythm continuously for 24 to 48 hours while you go about your daily life. For arrhythmias that happen only occasionally, an event monitor worn for weeks or even a small implantable loop recorder placed under the skin can catch episodes that would otherwise be missed.
Treatment Options
Treatment depends entirely on the type, severity, and underlying cause. Some arrhythmias need no treatment at all. Others require medication, a procedure, or an implanted device.
Medications
Several classes of drugs can help restore or maintain a normal rhythm. Some work by slowing electrical conduction through the heart. Others block the effects of adrenaline, reducing both heart rate and blood pressure. A third group targets specific electrical channels in heart cells (potassium or calcium channels) to stabilize the rhythm. The right choice depends on where the arrhythmia originates and what’s driving it.
Procedures and Devices
Catheter ablation is a procedure where a thin, flexible tube is threaded through a blood vessel to the heart. The tip delivers energy (heat or cold) to destroy the tiny area of tissue that’s sending faulty electrical signals. For younger patients with few other health problems, ablation is often the first-line option. It can restore normal rhythm and, in many cases, eliminate the need for long-term medication.
Pacemakers are small devices implanted under the skin near the collarbone. They monitor heart rhythm and deliver electrical impulses when the heart beats too slowly. For older patients with multiple health conditions, a pacemaker is often the more practical choice. An implantable cardioverter-defibrillator (ICD) works similarly but is designed for dangerous ventricular arrhythmias. It can deliver a stronger shock to reset the heart if it detects a life-threatening rhythm.
Reducing Your Risk
Many of the triggers for arrhythmia are things you can modify. Keeping blood pressure, cholesterol, and blood sugar in healthy ranges protects the heart’s structure and electrical system over time. Avoiding tobacco and limiting alcohol reduce direct triggers. If you take diuretics, staying hydrated and watching for signs of potassium loss (muscle cramps, weakness, fatigue) is particularly important, since even a short bout of vomiting or diarrhea can drop potassium levels enough to provoke an episode. Treating sleep apnea, managing stress, and staying physically active all contribute to a more stable rhythm.